Jasmonate signaling coordinates with the SOD7-KLU pathway to regulate seed size in Arabidopsis thaliana.

Seed size is crucial for crop yield and plant ecological fitness. The phytohormone jasmonate regulates Arabidopsis thaliana seed size, but the underlying molecular mechanisms remain elusive. Here, we established that CORONATINE INSENSITIVE1 (COI1)-mediated jasmonate signaling acts maternally to repress seed growth. Accordingly, jasmonate signaling suppresses the expression of KLUH (KLU), encoding an inducer of integument cell proliferation. KLU regulates the effects of COI1-mediated signaling on seed size. The JASMONATE ZIM-DOMAIN (JAZ) repressors of jasmonate signaling interact with SUPPRESSOR OF DA1-1 (SOD7) and DEVELOPMENT-RELATED PcG TARGET IN THE APEX4 (DPA4), two transcription factors that directly repress KLU. Overexpression of SOD7 largely rescues the seed size phenotype of coi1 mutants and JAZ1-overexpressing JAZ1-ΔJas plants. Furthermore, SOD7 associates with MYC2 and MYC4, two master transcriptional regulators of jasmonate signaling. SOD7 and MYC2 synergistically decrease KLU transcription and inhibit seed growth, while JAZ1 interferes with their transcriptional activities and physical interaction. Notably, jasmonate signaling considerably impacts seed size under salinity stress, primarily through SOD7 and KLU. Collectively, our findings suggest that the JAZ repressors and MYC transcription factors of the jasmonate signaling pathway coordinate with the SOD7/DPA4-KLU pathway to incorporate jasmonate signals into seed development.